DIYbanter - View Single Post

(John) wrote in message m...
I have just bought a house and a part of it has an earth floor. I
have plans to change it in to a garage or possibly a liveable area. I
am keen to learn a bit of DIY and my first job would be to lay a solid
floor where the earth currently is. I have never done any work with
concrete before and would be grateful of any advice on the best way of
doing things. How deep would I have to dig? What are the best ways to
waterproof the floor? The walls are damp and someone has suggested
laying a ventilated floor, does anyone have any advice about this?

This can definitely be DIY'd although I personally wouldn't make it my
first experience of using concrete. For a garage sized area do not
even think of mixing your own concrete, get it from a supplier, just
tell them what amount you need and what it is to be used for and let
them worry about the mix. Make sure you over order and have an area
for them to unload any unused excess onto as they will not keep any in
the mixer. Of course you have to have access for them to pump it into
your 'garage' but unless you are in a particularly peculiar situation
this is unlikely to be a problem. If you need to barrow it get some
help and lots of it. In general have enough help available so that you
and at least one helper do not have to be disturbed at any time from
doing the main job.

If it's a garage you will not need a insulation layer, but if it
becomes part of the 'liveable' part of the house you will by building
regs need to have one. You need to dig down about 300mm below the
required finish level. Lay, level and compact a 125-150mm scalpings
layer with a wacker (plate compacter, can be hired). Then lay a damp
proof membrane on this. This has to be lapped into the damp course of
the existing walls so make sure you leave enough at the edges to do
this. Oh wait, you said your walls are damp so chances are you will
need an injected DPC, something else you can hire and DIY. Now lay
50mm or whatever the building regs require of foam insulation board on
top of this. To get a level finish you can attach some insulation
board to the walls so the top of the board is at the floor finish
level. This is then used as a guide when you tamp down the concrete
for the final finish. You don't have to do this but the foam on the
walls also allows for expansion of the slab. If you don't do this then
attach some straight pieces of wood to the walls at the finish height,
AFTER you have lapped the DP membrane up the wall to achieve the same
effect. Then pump in a minimum of 100mm concrete on top of the board.
If it's going to be a garage 150mm of concrete should be the minimum.

Start putting concrete in at the end furthest away from the exit to
slightly above your finish level references and spread it about with a
rake. You will need a straight piece of wood shorter than the distance
between walls but long enough to sit on the reference foam/wood. Start
tamping from where the concrete first went in. Hold the piece of wood,
or more likely you and a helper hold the wood one at each end and in
short vertical movements compact (tamp) the concrete to the finish
level moving the wood toward you as you tamp and clear the top of the
reference levels of concrete so the tamping wood can sit on them as
you go.

After about half an hour to an hour after this is done you can start
troweling the surface smooth. You will need some largish boards to
kneel on so as not to sink into the still wet concrete. Do not over
trowel or the surface will end up dusty. The troweling should just
bring a small film of water to the surface if it's the right time to
start trowelling. When the concrete has had about 2 hours drying
spread sand over the whole surface to about 30mm deep and keep this
wet for at least a couple of days preferably a week to help the
concrete cure properly. If you are not confident at doing this, you
can finish at a level below the required final level, say 30mm and
make up the final level with a screed or sand/cement mix which you can
trowel over the concrete when it has dried. Or you can finish to a few
mm below your required level and when the concrete is dried buy a self
levelling screed which will make a nice final floor.

If you used wood reference levels these can be left in and screeded
over or removed and filled with concrete.

As far as the ventilated floor goes this is normally done using air
bricks placed into the walls under the level of a wooden suspended
floor. So I don't think it is relevant to you. Unless you decide to
make it a livable space in which case wood on joists is definitely the
best DIY way to go, much easier than messy and difficult concrete
work.

Steve.